An internal combustion engine is provided with an engine body, a catalyst device provided in an exhaust passage of the engine body and having an exhaust purification catalyst with at least an oxidation function and a microwave absorber contained in a catalyst coat layer formed inside a substrate, and a microwave emitter for irradiating the catalyst device with microwaves. A control device for the internal combustion engine is configured so that if engine startup is requested when a temperature of the exhaust purification catalyst is less than a predetermined temperature, it makes the microwave emitter irradiate the catalyst device with microwaves and operates the engine body so that an air-fuel ratio of exhaust discharged from the engine body becomes a predetermined lean air-fuel ratio leaner than a stoichiometric air-fuel ratio.